1. Field of the Invention
The present invention relates to ion implantation, and, more especially, to an apparatus and method for controlling a deflection of a charged particle beam.
2. Description of the Prior Art
Ion implanters are used in the manufacture of semiconductor devices and other materials. In such ion implanters, semiconductor wafers or other substrates are modified by implanting atoms of a desired species into the body of the wafer, for example to form regions of varying conductivity.
Charged particle filters, sometimes referred to as particle separators, are known in the art for the purpose of separating out unwanted particles from wanted particles in a particle beam. Generally, a sector magnetic field can be used to provide separation of charged particles by their momentum to charge ratio. Such devices are commonly used as mass analyzers and in mass spectrometry, to separate particles by mass when the energy and charge of the particles is assumed to be the same.
On the other hand, an electric field on its own may also be used for particle separation, in which case the filter acts as an energy filter for particles of the same charge state.
Considering in particular the application of charged particle filters to ion implanters, ion implanters using radio frequency acceleration to produce a beam of ions have a band of energies, so that an energy filter is required if the beam to be implanted is to have high energy purity. The use of a pure electrostatic energy filter which bends the accelerated beam through a predetermined angle in order to provide the required energy dispersion at an exit aperture of the filter, can work satisfactorily at high energies.
U.S. Pat. No. 6,946,667 provides an ion implantation apparatus including an ion source for extracting an ion beam to travel along an original ion beam path for implanting a target wafer; a set of deceleration electrodes disposed along the original ion beam path before the target wafer for decelerating and deflecting the ion beam to the target wafer; and a charged particle deflecting means, which generates a magnet field for filtering the ion beam, disposed between the ion source and the set of deceleration electrodes for deflecting the ion beam away from an original ion beam path and projecting to the set of electrodes with an incident angle relative to the original ion beam path. Here, the set of deceleration electrodes includes three pairs of electrodes arranged in sequence along an incident direction of the ion beam for generating an ion-beam filtering electric field.
U.S. Pat. No. 7,888,653 discloses a technique for independently controlling deflection, deceleration, and focus of an ion beam. The technique provides an electrode configuration including a set of entrance electrodes, one or more sets of suppression/focusing electrodes, and a set of exit electrodes. The potentials added for deflection to each set of electrodes are different and each set of electrodes may have a space/gap to allow an ion beam (e.g., a ribbon beam) to pass therethrough.
FIG. 1 depicts a side view of an electrode configuration in accordance with the U.S. Pat. No. 7,888,653. As shown in FIG. 1, the electrode configuration includes a set of entrance electrodes 302, five sets of suppression/focusing electrodes 304, and a set of exit electrodes 306. Each set of electrodes may have a space/gap to allow ion beam 30 to pass therethrough with a central ray trajectory. Here, each electrode is a regular electrode plate and the electrode configuration is a graded electrode configuration, such that each space/gap is the same along the central ray trajectory.
Besides the graded electrode configuration shown in FIG. 1, U.S. Pat. No. 7,888,653 also depicts that the electrode configuration is a flared electrode configuration or a parallel electrode configuration. In the flared electrode configuration of U.S. Pat. No. 7,888,653, as shown in FIG. 2, an opening for the ion beam 50 at the exit electrodes 506 may be greater than an opening for the ion beam 50 at the entrance electrodes 502. Accordingly, openings at each set of the suppression/focusing electrodes 504 may gradually increase or “flare” open.
In the parallel electrode configuration of U.S. Pat. No. 7,888,653, the upper electrodes are parallel with each other and the lower electrodes are parallel with each other. As shown in FIG. 3, the electrodes in the parallel lens configuration may be “flared” like the flared lens configuration of FIG. 2. For example, an opening for the ion beam 70 at the exit electrodes 706 may be greater than an opening for the ion beam 70 at the entrance electrodes 702. Accordingly, openings at each set of the suppression/focusing electrodes 704 may gradually increase or “flare” open.
In U.S. Pat. No. 7,888,653's disclosure, the upper and lower portions of suppression/focusing electrodes may all be regular shapes and each set of electrodes may be positioned symmetrically in its embodiment. Accordingly, the number of the upper suppression/focusing electrodes and the number of the lower suppression/focusing electrodes may be the same.
The foregoing set of deceleration electrodes disclosed by U.S. Pat. No. 6,946,667 and the one or more sets of suppression/focusing electrodes disclosed by U.S. Pat. No. 7,888,653 may not fine-tune the bend angle of the ion beam, so that the deflection of the ion beam may not be controlled with high efficiency.
The paper by O. A. Anderson, D. S. A Goldberg, W. S. Cooper, L. Soroka, “A Transverse Field Focusing (TFF) Accelerator for Intense Ribbon Ion Beam”, IEEE Trans. NS-30 No. 4, 1983, page 3215 discloses that a transverse electric field is set up between pairs of deflecting plates in TFF Accelerator. Here, the charged particles passing between the plates are both deflected and strongly focused by the field. Acceleration is achieved by adjusting the mean voltage on each succeeding pair of plates.